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    <title>Document</title>
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<body>
    <script>
        const reg = /^a(b|c)d\1$/
        console.log(reg.test("abdb"));//true
        console.log(reg.test("abbd"));//false
        
        const reg1 = /^a(b|c)(e|f)d\1\2$/
        console.log(reg1.test("abfdbf"));

    </script>
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